Lithium batteries are known to generate energy by converting to electrical energy the chemical energy resulting in the formation of lithium compounds from lithium atoms. The reactions for the formation of the lithium compounds may be reversed by feeding electrical energy to a lithium battery, in other words, most lithium batteries may be readily recharged. In conventional non-aqueous lithium batteries, the anodic reaction comprises lithium, which is often intercalated in fine particles of carbon, being ionized to form a mobile lithium ion accompanied by the generation of an electron. In the recharging step of the anode or negative electrode, lithium atom is reformed by consuming an electron. The cathodic reaction in the discharging step of most lithium batteries entails the formation of a lithium compound by reacting lithium ions with a compound capable of incorporating lithium in its structure and simultaneously consuming electrons. Most frequently the reactant compound utilized in the cathode or positive electrode is a lithiated transition metal oxide. Conveniently, the transition metal oxide is a vanadium oxide homologue, such as V.sub.6 O.sub.13, manganese dioxide, cobalt oxide, nickel oxide, tungsten dioxide and such like. In the recharging step of the cathode, lithium ions are released from the oxidic compound formed in the discharging reaction, simultaneously generating electrons.
The transition metal oxide for utilization as cathode active material in the positive electrode of a rechargeable lithium battery is required to be able to readily incorporate lithium ions in the discharging step and reversibly release the lithium ions in the charging step. Rechargeable lithium batteries utilizing lithium bearing manganese dioxide as the active component of the positive electrode are known, such batteries and methods for preparing crystalline lithium bearing manganese oxide utilized therein, are described for example, in U.S. Pat. No. 4,585,718 issued to S. Uedaira et al. on Apr. 29, 1986, and U.S. Pat. No. 4,758,485 issued to N. Furukawa et al. on Jul. 19, 1988. The preparation of lithium containing manganese oxide having particle size less than 20 .mu.m and specific surface area in a certain desirable range, by heat-treatment at 375.degree. C. of a mixture of fine dry lithium hydroxide and manganese dioxide, is described in U.S. Pat. No. 5,294,499, issued to N. Furukawa et al. on Mar. 15, 1994. Thackaray et al. in Canadian patent 1,331,506, issued on Aug. 23, 1994, teach the preparation of lithium deficient lithium-manganese oxide having the general formula Li.sub.1-x Mn.sub.2 O.sub.4, where x has a value which is greater than zero but less than one, and the subsequent heat-treatment of the mixed oxides at temperatures higher than 200.degree. C. The lithium-manganese oxide obtained in accordance with Thackaray et al. has a spinel-type crystal structure. The preparation of spinel-type small particle size Li.sub.1-x Mn.sub.2 O.sub.4, where the value of x ranges between zero and one, from organic precursors at temperatures higher than 300.degree. C. and their performance in a lithium battery, are described in U.S. Pat. No. 5,135,732, issued to Barboux et al. on Apr. 23, 1991. It is noted that the lithium-manganese dioxide compound obtained by any of the methods described in the publications referred to hereinabove, was fully crystalline which was indicated in the referred publications by X-ray diffraction identification of characteristic peaks.
It has been observed that while the expected open circuit voltage of a lithium battery can be attained after repeated charge-discharge cycles of a transition metal oxide bearing lithium battery, the energy density obtained may often diminish in the repeated cycling of such lithium batteries. It is the object of this invention to provide a new form of lithium-manganese oxide containing positive electrode for utilization in a non-aqueous rechargeable lithium battery, which is capable of maintaining high energy density in repeated charging-recharging cycles.